A novel biomarker for staging human prostate adenocarcinoma: overexpression of matriptase with concomitant loss of its inhibitor, hepatocyte growth factor activator inhibitor-1

Loss of hepatocyte growth factor activator inhibitor type 1 participates in metastatic spreading of human pancreatic cancer cells in a mouse orthotopic transplantation model

Hepatocyte growth factor activator inhibitor type 1 (HAI-1) is a membrane-bound serine protease inhibitor that is expressed on the surface of epithelial and carcinoma cells. On the cell surface, HAI-1 regulates membrane-anchored serine proteases, with matriptase being the most critical target. Matriptase is involved in pericellular processing of biologically active molecules, including protease-activated receptor-2 (PAR-2). Previously we reported that S2-CP8 cells, a metastatic variant of the SUIT-2 human pancreatic adenocarcinoma cell line, showed markedly decreased HAI-1 expression. To assess the significance of HAI-1 loss in invasion and spontaneous metastasis of S2-CP8 cells, we established stable S2-CP8 sublines that expressed HAI-1 under the control of a tetracycline-regulated promoter. In vitro migration and invasion assays revealed inhibitory effects of HAI-1 on S2-CP8 cell migration and invasion. Matriptase activity was suppressed by the expression of HAI-1. As the enhanced invasiveness in the absence of HAI-1 was alleviated by knockdown of matriptase by 81% and of PAR-2 completely, and PAR-2 antagonist also suppressed the invasion, matriptase-mediated PAR-2 activation is involved in HAI-1 loss-induced invasion of S2-CP8 cells. We then analyzed the effect of HAI-1 expression on metastasis of S2-CP8 cells in vivo using a nude mouse orthotopic xenograft model. Although approximately 50% of the control mice developed distant metastasis, mice treated with doxycycline to induce HAI-1 expression did not develop metastasis. These data indicate that HAI-1 loss contributes to invasion and dissemination of a highly metastatic subline of SUIT-2, suggesting crucial roles for the balance of pericellular serine proteases/inhibitors in pancreatic cancer progression.

Overexpression of matriptase correlates with poor prognosis in esophageal squamous cell carcinoma

Matriptase is one of the type II transmembrane serine proteases and is known to be involved in cancer progression. Increased matriptase expression has been reported in a variety of human cancers, and its association with poor prognosis has been highlighted in some cancer types. However, its exact role in cancer progression and its effect on patient survival in esophageal squamous cell carcinoma (ESCC) are still unclear. We performed immunohistochemical staining of matriptase in 171 ESCC samples after antibody validation and evaluated the association of its expression with clinicopathological parameters and prognosis. High matriptase expression was observed in 38.6 % (66/171) of ESCC samples and more frequently in N3 stage and in poorly differentiated tumors. Both overall survival (OS) and disease-free survival (DFS) were significantly lower for patients with high expression of matriptase than for patients with low expression (5-year OS rate, 38.6 vs 55.3 %; p=0.034 and 5-year DFS rate, 30.5 vs 49.4 %; p=0.007). High matriptase expression was an independent prognostic factor for OS [hazard ratio (HR), 1.65 (95 % confidence interval (CI), 1.01-2.68); p=0.045] and for DFS [HR, 1.79 (95 % CI, 1.14-2.81); p=0.012]. In conclusion, higher expression of matriptase is an independent prognostic factor involved in the progression of ESCC, which suggests that matriptase is a factor in ESCC tumor progression and also a potential molecular therapeutic target.

HAI-2 suppresses the invasive growth and metastasis of prostate cancer through regulation of matriptase

Dysregulation of cell surface proteolysis has been strongly implicated in tumorigenicity and metastasis. In this study, we delineated the role of hepatocyte growth factor activator inhibitor-2 (HAI-2) in prostate cancer (PCa) cell migration, invasion, tumorigenicity and metastasis using a human PCa progression model (103E, N1, and N2 cells) and xenograft models. N1 and N2 cells were established through serial intraprostatic propagation of 103E human PCa cells and isolation of the metastatic cells from nearby lymph nodes. The invasion capability of these cells was revealed to gradually increase throughout the serial isolations (103E<N1<N2). In this series of cells, the expression of HAI-2 but not HAI-1 was significantly decreased throughout the progression and occurred in parallel with increased activation of matriptase. The expression level and activity of matriptase increased whereas the HAI-2 protein level decreased over the course of orthotopic tumor growth in mice, which was consistent with the immunohistochemical profiles of matriptase and HAI-2 in archival PCa specimens. Knockdown of matriptase reduced the PCa cell invasion induced by HAI-2 knockdown. HAI-2 overexpression or matriptase silencing in N2 cells downregulated matriptase activity and significantly decreased tumorigenicity and metastatic capability in orthotopically xenografted mice. These results suggest that during the progression of human PCa, matriptase activity is primarily controlled by HAI-2 expression. The imbalance between HAI-2 and matriptase expression led to matriptase activation, thereby increasing cell migration, invasion, tumorigenicity and metastasis.

Combinatorial optimization of cystine-knot peptides towards high-affinity inhibitors of human matriptase-1

Cystine-knot miniproteins define a class of bioactive molecules with several thousand natural members. Their eponymous motif comprises a rigid structured core formed by six disulfide-connected cysteine residues, which accounts for its exceptional stability towards thermic or proteolytic degradation. Since they display a remarkable sequence tolerance within their disulfide-connected loops, these molecules are considered promising frameworks for peptide-based pharmaceuticals. Natural open-chain cystine-knot trypsin inhibitors of the MCoTI (Momordica cochinchinensis trypsin inhibitor) and SOTI (Spinacia oleracea trypsin inhibitor) families served as starting points for the generation of inhibitors of matriptase-1, a type II transmembrane serine protease with possible clinical relevance in cancer and arthritic therapy. Yeast surface-displayed libraries of miniproteins were used to select unique and potent matriptase-1 inhibitors. To this end, a knowledge-based library design was applied that makes use of detailed information on binding and folding behavior of cystine-knot peptides. Five inhibitor variants, four of the MCoTI family and one of the SOTI family, were identified, chemically synthesized and oxidatively folded towards the bioactive conformation. Enzyme assays revealed inhibition constants in the low nanomolar range for all candidates. One subnanomolar binder (K_i = 0.83 nM) with an inverted selectivity towards trypsin and matriptase-1 was identified.

The S100A4 Oncoprotein Promotes Prostate Tumorigenesis in a Transgenic Mouse Model: Regulating NFκB through the RAGE Receptor

S100A4, a calcium-binding protein, is known for its role in the metastatic spread of tumor cells, a late event of cancer disease. This is the first report showing that S100A4 is not merely a metastatic protein but also an oncoprotein that plays a critical role in the development of tumors. We earlier showed that S100A4 expression progressively increases in prostatic tissues with the advancement of prostate cancer (CaP) in TRAMP, an autochthonous mouse model. To study the functional significance of S100A4 in CaP, we generated a heterozygously deleted S100A4 (TRAMP/S100A4(+/-)) genotype by crossing TRAMP with S100A4(-/-) mice. TRAMP/S100A4(+/-) did not show a lethal phenotype, and transgenes were functional. As compared to age-matched TRAMP littermates, TRAMP/S100A4(+/-) mice exhibited 1) an increased tumor latency period (P < 0.001), 2) a 0% incidence of metastasis, and 3) reduced prostatic weights (P < 0.001). We generated S100A4-positive clones from S100A4-negative CaP cells and tested their potential. S100A4-positive tumors grew at a faster rate than S100A4-negative tumors in vitro and in a xenograft mouse model. The S100A4 protein exhibited growth factor-like properties in multimode (intracellular and extracellular) forms. We observed that 1) the growth-promoting effect of S100A4 is due to its activation of NFκB, 2) S100A4-deficient tumors exhibit reduced NFκB activity, 3) S100A4 regulates NFκB through the RAGE receptor, and 4) S100A4 and RAGE co-localize in prostatic tissues of mice. Keeping in view its growth-promoting role, we suggest that S100A4 qualifies as an excellent candidate to be exploited for therapeutic agents to treat CaP in humans.

BMI1 polycomb group protein acts as a master switch for growth and death of tumor cells: regulates TCF4-transcriptional factor-induced BCL2 signaling

For advanced prostate cancer (CaP), the progression of tumors to the state of chemoresistance and paucity of knowledge about the mechanism of chemoresistance are major stumbling blocks in the management of this disease. Here, we provide compelling evidence that BMI1 polycomb group protein and a stem cell factor plays a crucial role in determining the fate of tumors vis-à-vis chemotherapy. We show that progressive increase in the levels of BMI1 occurs during the progression of CaP disease in humans. We show that BMI1-rich tumor cells are non-responsive to chemotherapy whereas BMI1-silenced tumor cells are responsive to therapy. By employing microarray, ChIP, immunoblot and Luciferase reporter assays, we identified a unique mechanism through which BMI1 rescues tumor cells from chemotherapy. We found that BMI1 regulates (i) activity of TCF4 transcriptional factor and (ii) binding of TCF4 to the promoter region of anti-apoptotic BCL2 gene. Notably, an increased TCF4 occupancy on BCL2 gene was observed in prostatic tissues exhibiting high BMI1 levels. Using tumor cells other than CaP, we also showed that regulation of TCF4-mediated BCL2 by BMI1 is universal. It is noteworthy that forced expression of BMI1 was observed to drive normal cells to hyperproliferative mode. We show that targeting BMI1 improves the outcome of docetaxel therapy in animal models bearing chemoresistant prostatic tumors. We suggest that BMI1 could be exploited as a potential molecular target for therapeutics to treat chemoresistant tumors.

Curcumin-targeting pericellular serine protease matriptase role in suppression of prostate cancer cell invasion, tumor growth, and metastasis

Curcumin has been shown to possess potent chemopreventive and antitumor effects on prostate cancer. However, the molecular mechanism involved in curcumin's ability to suppress prostate cancer cell invasion, tumor growth, and metastasis is not yet well understood. In this study, we have shown that curcumin can suppress epidermal growth factor (EGF)- stimulated and heregulin-stimulated PC-3 cell invasion, as well as androgen-induced LNCaP cell invasion. Curcumin treatment significantly resulted in reduced matrix metalloproteinase 9 activity and downregulation of cellular matriptase, a membrane-anchored serine protease with oncogenic roles in tumor formation and invasion. Our data further show that curcumin is able to inhibit the induction effects of androgens and EGF on matriptase activation, as well as to reduce the activated levels of matriptase after its overexpression, thus suggesting that curcumin may interrupt diverse signal pathways to block the protease. Furthermore, the reduction of activated matriptase in cells by curcumin was also partly due to curcumin's effect on promoting the shedding of matriptase into an extracellular environment, but not via altering matriptase gene expression. In addition, curcumin significantly suppressed the invasive ability of prostate cancer cells induced by matriptase overexpression. In xenograft model, curcumin not only inhibits prostate cancer tumor growth and metastasis but also downregulates matriptase activity in vivo. Overall, the data indicate that curcumin exhibits a suppressive effect on prostate cancer cell invasion, tumor growth, and metastasis, at least in part via downregulating matriptase function.

Crystal structures of matriptase in complex with its inhibitor hepatocyte growth factor activator inhibitor-1

Matriptase, a type II trans-membrane serine protease of the S1 trypsin-like family, is expressed on the surface of nearly all normal human epithelium and found in biological fluid-like human milk. Matriptase overexpression has been implicated in tumor progression in certain epithelium-derived cancer cells. Matriptase is tightly regulated by its cognate inhibitor hepatocyte growth factor activator inhibitor-1 (HAI-1). It has been demonstrated that the Kunitz domain I (KD1) but not Kunitz domain II (KD2) of HAI-1 is responsible for the inhibitory activity of HAI-1 against matriptase. To investigate the molecular basis of inhibition of matriptase by HAI-1, we solved several crystal structures of matriptase serine protease domain in complex with the fragments of HAI-1. Based on these structures, we found that the binding of KD1 was different from previously predicted binding mode. The P3 arginine residue occupies the S3 specificity pocket of matriptase, but not the S4 pocket as in the cases of hepatocyte growth factor activator·HAI-1 KD1 and matriptase·sunflower trypsin inhibitor-1 complexes. The long 60-loop of matriptase makes direct contact with HAI-1 but remains flexible even in the complexes, and its apex does not bind with KD1 tightly. The interactions between this unique 60-loop and KD1 may provide an opportunity to increase the specificity and inhibitory activity of KD1 for matriptase. Furthermore, comparison between KD1 and a homology model of HAI-1 KD2 rationalizes the structural basis of why KD1 but not KD2 is responsible for the inhibitory activity of HAI-1 against matriptase.

ARHGAP21 is a RhoGAP for RhoA and RhoC with a role in proliferation and migration of prostate adenocarcinoma cells

BACKGROUND

Several Rho GTPase-activating proteins (RhoGAPs) are implicated in tumor progression through their effects on Rho GTPase activity. ARHGAP21 is a RhoGAP with increased expression in head and neck squamous cell carcinoma and with a possible role in glioblastoma tumor progression, yet little is known about the function of ARHGAP21 in cancer cells. Here we studied the role of ARHGAP21 in two prostate adenocarcinoma cell lines, LNCaP and PC3, which respectively represent initial and advanced stages of prostate carcinogenesis.

RESULTS

ARHGAP21 is located in the nucleus and cytoplasm of both cell lines and its depletion resulted in decreased proliferation and increased migration of PC3 cells but not LNCaP cells. In PC3 cells, ARHGAP21 presented GAP activity for RhoA and RhoC and induced changes in cell morphology. Moreover, its silencing altered the expression of genes involved in cell proliferation and cytoskeleton organization, as well as the endothelin-1 canonical pathway.

CONCLUSIONS

Our results reveal new functions and signaling pathways regulated by ARHGAP21, and indicate that it could contribute to prostate cancer progression.

BMI1, stem cell factor acting as novel serum-biomarker for Caucasian and African-American prostate cancer

BACKGROUND

Lack of reliable predictive biomarkers is a stumbling block in the management of prostate cancer (CaP). Prostate-specific antigen (PSA) widely used in clinics has several caveats as a CaP biomarker. African-American CaP patients have poor prognosis than Caucasians, and notably the serum-PSA does not perform well in this group. Further, some men with low serum-PSA remain unnoticed for CaP until they develop disease. Thus, there is a need to identify a reliable diagnostic and predictive biomarker of CaP. Here, we show that BMI1 stem-cell protein is secretory and could be explored for biomarker use in CaP patients.

METHODOLOGY/PRINCIPAL FINDINGS

Semi-quantitative analysis of BMI1 was performed in prostatic tissues of TRAMP (autochthonous transgenic mouse model), human CaP patients, and in cell-based models representing normal and different CaP phenotypes in African-American and Caucasian men, by employing immunohistochemistry, immunoblotting and Slot-blotting. Quantitative analysis of BMI1 and PSA were performed in blood and culture-media of siRNA-transfected and non-transfected cells by employing ELISA. BMI1 protein is (i) secreted by CaP cells, (ii) increased in the apical region of epithelial cells and stromal region in prostatic tumors, and (iii) detected in human blood. BMI1 is detectable in blood of CaP patients in an order of increasing tumor stage, exhibit a positive correlation with serum-PSA and importantly is detectable in patients which exhibit low serum-PSA. The clinical significance of BMI1 as a biomarker could be ascertained from observation that CaP cells secrete this protein in higher levels than cells representative of benign prostatic hyperplasia (BPH).

CONCLUSIONS/SIGNIFICANCE

BMI1 could be developed as a dual bio-marker (serum and biopsy) for the diagnosis and prognosis of CaP in Caucasian and African-American men. Though compelling these data warrant further investigation in a cohort of African-American patients.

Imaging a functional tumorigenic biomarker in the transformed epithelium

Proteases responsible for the increased peritumoral proteolysis associated with cancer represent functional biomarkers for monitoring tumorigenesis. One attractive extracellular biomarker is the transmembrane serine protease matriptase. Found on the surface of epithelial cells, the activity of matriptase is regulated by its cognate inhibitor hepatocyte growth factor activator inhibitor-1 (HAI-1). Quantitative mass spectrometry allowed us to show that, in selected cancers, HAI-1 expression decreases, leading to active matriptase. A preclinical probe specific for the measurement of emergent active matriptase was developed. Using an active-site-specific, recombinant human antibody for matriptase, we found that the selective targeting of active matriptase can be used to visualize the tumorigenic epithelium. Live-cell fluorescence imaging validated the selectivity of the antibody in vitro by showing that the probe localized only to cancer cell lines with active matriptase on the surface. Immunofluorescence with the antibody documented significant levels of active matriptase in 68% of primary and metastatic colon cancer sections from tissue microarrays. Labeling of the active form of matriptase in vivo was measured in human colon cancer xenografts and in a patient-derived xenograft model using near-infrared and single-photon emission computed tomography imaging. Tumor uptake of the radiolabeled antibody, (111)In-A11, by active matriptase was high in xenografts (28% injected dose per gram) and was blocked in vivo by the addition of a matriptase-specific variant of ecotin. These findings suggest, through a HAI-1-dependent mechanism, that emergent active matriptase is a functional biomarker of the transformed epithelium and that its proteolytic activity can be exploited to noninvasively evaluate tumorigenesis in vivo.

From prediction to experimental validation: desmoglein 2 is a functionally relevant substrate of matriptase in epithelial cells and their reciprocal relationship is important for cell adhesion

Accurate identification of substrates of a protease is critical in defining its physiological functions. We previously predicted that Dsg-2 (desmoglein-2), a desmosomal protein, is a candidate substrate of the transmembrane serine protease matriptase. The present study is an experimental validation of this prediction. As demanded by our published method PNSAS [Prediction of Natural Substrates from Artificial Substrate of Proteases; Venkatraman, Balakrishnan, Rao, Hooda and Pol (2009) PLoS ONE 4, e5700], this enzyme-substrate pair shares a common subcellular distribution and the predicted cleavage site is accessible to the protease. Matriptase knock-down cells showed enhanced immunoreactive Dsg-2 at the cell surface and formed larger cell clusters. When matriptase was mobilized from intracellular storage deposits to the cell surface there was a decrease in the band intensity of Dsg-2 in the plasma membrane fractions with a concomitant accumulation of a cleaved product in the conditioned medium. The exogenous addition of pure active recombinant matriptase decreased the surface levels of immunoreactive Dsg-2, whereas the levels of CD44 and E-cadherin were unaltered. Dsg-2 with a mutation at the predicted cleavage site is resistant to cleavage by matriptase. Thus Dsg-2 seems to be a functionally relevant physiological substrate of matriptase. Since breakdown of cell-cell contact is the first major event in invasion, this reciprocal relationship is likely to have a profound role in cancers of epithelial origin. Our algorithm has the potential to become an integral tool for discovering new protease-substrate pairs.

Chemical synthesis, backbone cyclization and oxidative folding of cystine-knot peptides: promising scaffolds for applications in drug design

Cystine-knot peptides display exceptional structural, thermal, and biological stability. Their eponymous motif consists of six cysteine residues that form three disulfide bonds, resulting in a notably rigid structural core. Since they highly tolerate either rational or combinatorial changes in their primary structure, cystine knots are considered to be promising frameworks for the development of peptide-based pharmaceuticals. Despite their relatively small size (two to three dozens amino acid residues), the chemical synthesis route is challenging since it involves critical steps such as head-to-tail cyclization and oxidative folding towards the respective bioactive isomer. Herein we describe the topology of cystine-knot peptides, their synthetic availability and briefly discuss potential applications of engineered variants in diagnostics and therapy.

Mechanisms for the control of matriptase activity in the absence of sufficient HAI-1

Matriptase proteolytic activity must be tightly controlled for normal placental development, epidermal function, and epithelial integrity. Although hepatocyte growth factor activator inhibitor-1 (HAI-1) represents the predominant endogenous inhibitor for matriptase and the protein molar ratio of HAI-1 to matriptase is determined to be >10 in epithelial cells and the majority of carcinoma cells, an inverse HAI-1-to-matriptase ratio is seen in some ovarian and hematopoietic cancer cells. In the current study, cells with insufficient HAI-1 are investigated for the mechanisms through which the activity of matriptase is regulated. When matriptase activation is robustly induced in these cells, activated matriptase rapidly forms two complexes of 100- and 140-kDa in addition to the canonical 120-kDa matriptase-HAI-1 complex already described. Both 100- and 140-kDa complexes contain two-chain, cleaved matriptase but are devoid of gelatinolytic activity. Further biochemical characterization shows that the 140-kDa complex is a matriptase homodimer and that the 100-kDa complexes appear to contain reversible, tight binding serine protease inhibitor(s). The formation of the 140-kDa matriptase dimer is strongly associated with matriptase activation, and its levels are inversely correlated with the ratio of HAI-1 to matriptase. Given these observations and the likelihood that autoactivation requires the interaction of two matriptase molecules, it seems plausible that this activated matriptase homodimer may represent a matriptase autoactivation intermediate and that its accumulation may serve as a mechanism to control matriptase activity when protease inhibitor levels are limiting. These data suggest that matriptase activity can be rapidly inhibited by HAI-1 and other HAI-1-like protease inhibitors and "locked" in an inactive autoactivation intermediate, all of which places matriptase under very tight control.

Targeting zymogen activation to control the matriptase-prostasin proteolytic cascade

Membrane-associated serine protease matriptase has been implicated in human diseases and might be a drug target. In the present study, a novel class of matriptase inhibitors targeting zymogen activation is developed by a combination of the screening of compound library using a cell-based matriptase activation assay and a computer-aided search of commercially available analogues of a selected compound. Four structurally related compounds are identified that can inhibit matriptase activation with IC(50) at low micromolar concentration in both intact-cell and cell-free systems, suggesting that these inhibitors target the matriptase autoactivation machinery rather than the intracellular signaling pathways. These activation inhibitors can also inhibit prostasin activation, a downstream event that occurs in lockstep with matriptase activation. In contrast, the matriptase catalytic inhibitor CVS-3983 at a concentration 300-fold higher than its K(i) fails to inhibit activation of either protease. Our results suggest that inhibiting matriptase activation is an efficient way to control matriptase function.

Matriptase is inhibited by extravascular antithrombin in epithelial cells but not in most carcinoma cells

Antithrombin, a major anticoagulant, is robustly transported into extravascular compartments where its target proteases are largely unknown. This serpin was previously detected in human milk as complexes with matriptase, a membrane-bound serine protease broadly expressed in epithelial and carcinoma cells, and under tight regulation by hepatocyte growth factor activator inhibitor (HAI)-1, a transmembrane Kunitz-type serine protease inhibitor that forms heat-sensitive complexes with active matriptase. In the current study, we detect, in addition to matriptase-HAI-1 complexes, heat-resistant matriptase complexes generated by nontransformed mammary, prostate, and epidermal epithelial cells that we show to be matriptase-antithrombin complexes. These findings suggest that in addition to HAI-1, interstitial antithrombin participates in the regulation of matriptase activity in epithelial cells. This physiological mechanism appears, however, to largely be lost in cancer cells since matriptase-antithrombin complexes were not detected in all but two of a panel of seven breast, prostate, and ovarian cancer cell lines. Using purified active matriptase, we further characterize the formation of matriptase-antithrombin complex and show that heparin can significantly potentiate the inhibitory potency of antithrombin against matriptase. Second-order rate constants for the inhibition were determined to be 3.9 × 10(3) M(-1)s(-1) in the absence of heparin and 1.2 × 10(5) M(-1)s(-1) in the presence of heparin, a 30-fold increase, consistent with the established role of heparin in activating antithrombin function. Taken together these data suggest that normal epithelial cells employ a dual mechanism involving HAI-1 and antithrombin to control matriptase and that the antithrombin-based mechanism appears lost in the majority of carcinoma cells.

Membrane-anchored serine proteases in health and disease

Serine proteases of the trypsin-like family have long been recognized to be critical effectors of biological processes as diverse as digestion, blood coagulation, fibrinolysis, and immunity. In recent years, a subgroup of these enzymes has been identified that are anchored directly to plasma membranes, either by a carboxy-terminal transmembrane domain (Type I), an amino-terminal transmembrane domain with a cytoplasmic extension (Type II or TTSP), or through a glycosylphosphatidylinositol (GPI) linkage. Recent biochemical, cellular, and in vivo analyses have now established that membrane-anchored serine proteases are key pericellular contributors to processes vital for development and the maintenance of homeostasis. This chapter reviews our current knowledge of the biological and physiological functions of these proteases, their molecular substrates, and their contributions to disease.

TMPRSS2/ERG promotes epithelial to mesenchymal transition through the ZEB1/ZEB2 axis in a prostate cancer model

Prostate cancer is the most common non-dermatologic malignancy in men in the Western world. Recently, a frequent chromosomal aberration fusing androgen regulated TMPRSS2 promoter and the ERG gene (TMPRSS2/ERG) was discovered in prostate cancer. Several studies demonstrated cooperation between TMPRSS2/ERG and other defective pathways in cancer progression. However, the unveiling of more specific pathways in which TMPRSS2/ERG takes part, requires further investigation. Using immortalized prostate epithelial cells we were able to show that TMPRSS2/ERG over-expressing cells undergo an Epithelial to Mesenchymal Transition (EMT), manifested by acquisition of mesenchymal morphology and markers as well as migration and invasion capabilities. These findings were corroborated in vivo, where the control cells gave rise to discrete nodules while the TMPRSS2/ERG-expressing cells formed malignant tumors, which expressed EMT markers. To further investigate the general transcription scheme induced by TMPRSS2/ERG, cells were subjected to a microarray analysis that revealed a distinct EMT expression program, including up-regulation of the EMT facilitators, ZEB1 and ZEB2, and down-regulation of the epithelial marker CDH1(E-Cadherin). A chromatin immunoprecipitation assay revealed direct binding of TMPRSS2/ERG to the promoter of ZEB1 but not ZEB2. However, TMPRSS2/ERG was able to bind the promoters of the ZEB2 modulators, IL1R2 and SPINT1. This set of experiments further illuminates the mechanism by which the TMPRSS2/ERG fusion affects prostate cancer progression and might assist in targeting TMPRSS2/ERG and its downstream targets in future drug design efforts.

Structure of catalytic domain of Matriptase in complex with Sunflower trypsin inhibitor-1

Background

Matriptase is a type II transmembrane serine protease that is found on the surfaces of epithelial cells and certain cancer cells. Matriptase has been implicated in the degradation of certain extracellular matrix components as well as the activation of various cellular proteins and proteases, including hepatocyte growth factor and urokinase. Sunflower trypsin inhibitor-1 (SFTI-1), a cyclic peptide inhibitor originally isolated from sunflower seeds, exhibits potent inhibitory activity toward matriptase.

Results

We have engineered and produced recombinant proteins of the matriptase protease domain, and have determined the crystal structures of the protease:SFTI-1 complex at 2.0 Å as well as the protease:benzamidine complex at 1.2 Å. These structures elaborate the structural basis of substrate selectivity of matriptase, and show that the matriptase S1 substrate specificity pocket is larger enough to allow movement of benzamidine inside the S1 pocket. Our study also reveals that SFTI-1 binds to matriptase in a way similar to its binding to trypsin despite the significantly different isoelectric points of the two proteins (5.6 vs. 8.2).

Conclusions

This work helps to define the structural basis of substrate specificity of matriptase and the interactions between the inhibitor and protease. The complex structure also provides a structural template for designing new SFTI-1 derivatives with better potency and selectivity against matriptase and other proteases.

Laminin-332 cleavage by matriptase alters motility parameters of prostate cancer cells

BACKGROUND

Matriptase, a type II transmembrane serine protease, has been linked to initiation and promotion of epidermal carcinogenesis in a murine model, suggesting that deregulation of its role in epithelia contributes to transformation. In human prostate cancer, matriptase expression correlates with progression. It is therefore of interest to determine how matriptase may contribute to epithelial neoplastic progression. One approach for studying this is to identify potential matriptase substrates involved in epithelial integrity and/or transformation like the extracellular matrix macromolecule, laminin-332 (Ln-332), which is found in the basement membrane of many epithelia, including prostate. Proteolytic processing of Ln-332 regulates cell motility of both normal and transformed cells, which has implications in cancer progression.

METHODS

In vitro cleavage experiments were performed with purified Ln-332 protein and matriptase. Western blotting, enzyme inhibition assays, and mass spectrometry were used to confirm cleavage events. Matriptase overexpressing LNCaP prostate cancer cells were generated and included in Transwell migration assays and single cell motility assays, along with other prostate cells.

RESULTS

We report that matriptase proteolytically cleaves Ln-332 in the β3 chain. Substrate specificity was confirmed by blocking cleavage with the matriptase inhibitor, Kunitz domain-1. Transwell migration assays showed that DU145 cell motility was significantly enhanced when plated on matriptase-cleaved Ln-332. Similarly, Transwell migration of matriptase-overexpressing LNCaP cells was significantly increased on Ln-332 and, as determined by live single-cell microscopy, two motility parameters of this cell line, speed and directional persistence, were also higher.

CONCLUSIONS

Proteolytic processing of Ln-332 by matriptase enhances speed and directional persistence of prostate cancer cells.

Hepatocyte growth factor activator inhibitor type 1 suppresses metastatic pulmonary colonization of pancreatic carcinoma cells

Hepatocyte growth factor activator inhibitor type 1 (HAI-1) is a transmembrane protease inhibitor that regulates the activities of membrane-bound and extracellular serine proteases. HAI-1 has two Kunitz-type inhibitor domains with the N-terminal Kunitz domain (KD1) responsible for inhibiting known target proteases. Previously, we reported that knockdown of HAI-1 in the human pancreatic carcinoma cell line SUIT-2 resulted in epithelial to mesenchymal transition. To evaluate the role of HAI-1 in metastasis, we examined the metastatic capability of SUIT-2 cells that did or did not stably express HAI-1 short-hairpin RNA in an experimental pulmonary metastasis assay using nude mice. The extent of pulmonary metastasis was verified by histological examination and direct measurement of human cytokeratin 19 mRNA levels. One week after injecting SUIT-2 cells into mouse tail veins, apparent metastatic colonization was observed in 36% (4/11) of mice injected with HAI-1-knockdown SUIT-2, whereas none (0/11) of the control mice were positive for metastasis. After 2 weeks the metastasis positive ratios were 80% (4/5) and 40% (2/5), and after 4 weeks the ratios were 82% (9/11) and 45% (5/11) for HAI-1-knockdown and control SUIT-2 cells, respectively. Thus, loss of HAI-1 promoted pulmonary metastasis. Co-injection of recombinant KD1 abolished metastasis produced by HAI-1-knockdown SUIT-2 cells after 1 week. Moreover, recombinant KD1 restored E-cadherin levels in HAI-1 knockdown SUIT-2 cells and reduced their invasiveness in vitro. These data indicate that HAI-1 regulates pulmonary metastasis of SUIT-2, and KD1 may have therapeutic application for inhibiting metastatic cancer cell spreading.

A novel signaling axis of matriptase/PDGF-D/ß-PDGFR in human prostate cancer

Increasing evidence indicates the significance of platelet-derived growth factor receptor-β (β-PDGFR) signaling in prostate cancer (PCa). Accordingly, preclinical studies suggest the potential of β-PDGFR as a therapeutic target in metastatic PCa. However, a ligand responsible for β-PDGFR activation in PCa was unknown, and recent clinical trials with imatinib mesylate showed limited success due to normal tissue toxicity. Similarly, in spite of mounting evidence indicating the significance of matriptase in PCa, little is known about its substrates or molecular actions during PCa progression. Here, we identified PDGF-D as a ligand for β-PDGFR in PCa and discovered matriptase as its regulator. Matriptase activates PDGF-D by proteolytic removal of the CUB domain in a 2-step process, creating a hemidimer, followed by growth factor domain dimer (GFD-D) generation. Matriptase can deactivate PDGF-D by further proteolytic cleavage within the GFD, revealing its biphasic regulation. Importantly, PDGF-D/matriptase colocalization is accompanied with β-PDGFR phosphorylation in human PCa tissues. This study unveiled a novel signaling axis of matriptase/PDGF-D/β-PDGFR in PCa, providing new insights into functional interplay between serine protease and growth factor signaling networks.

Matriptase is involved in ErbB-2-induced prostate cancer cell invasion

Deregulation of both ErbB-2 signaling and matriptase activity has been associated with human prostate cancer (PCa) progression. In this communication, we investigated the roles of both ErbB-2 signaling in matriptase zymogen activation and matriptase in ErbB-2-induced PCa malignancy. In a human PCa cell progression model, we observed that advanced PCa C-81 LNCaP cells exhibited an aggressive phenotype with increased cell migration and invasion capacity; these cells concurrently showed both enhanced ErbB-2 phosphorylation and increased matriptase zymogen activation compared with parental C-33 LNCaP cells. Moreover, ErbB2 activation, both ligand-dependent (eg, epidermal growth factor treatment) and ligand-independent (eg, overexpression), was able to induce matriptase zymogen activation in this cell line. Inhibition of ErbB-2 activity by either the specific inhibitor, AG825, in epidermal growth factor-treated C-33 LNCaP cells or ErbB-2 knockdown in C-81 LNCaP cells, reduced matriptase activation. These observations were confirmed by similar studies using both DU145 and PC3 cells. Together, these data suggest that ErbB-2 signaling plays an important role in matriptase zymogen activation. ErbB-2-enhanced matriptase activation was suppressed by a phosphatidylinositol 3-kinase inhibitor (ie, LY294002) but not by a MEK inhibitor (ie, PD98059). Suppression of matriptase expression by small hairpin RNA knockdown in ErbB-2-overexpressing LNCaP cells dramatically suppressed cancer cell invasion. In summary, our data indicate that ErbB-2 signaling via the phosphatidylinositol 3-kinase pathway results in up-regulated matriptase zymogen activity, which contributes to PCa cell invasion.

The role of hepatocyte growth factor activator inhibitor (HAI)-1 and HAI-2 in endometrial cancer

Hepatocyte growth factor activator inhibitors (HAI-1 and HAI-2) are Kunitz-type serine protease inhibitors that have a broad inhibitory spectrum against serine proteases. This is the first study to investigate the role of HAI-1 and HAI-2 in endometrial cancer. We investigated the biological functions of HAI-1 and HAI-2 using KLE and HEC-251 endometrial cancer cell lines, thus HAI-1 and HAI-2 were examined in uterine normal endometrium, endometrial hyperplasia and cancer specimens by immunohistochemistry. HAI-1 and HAI-2 showed potential inhibitory effects on cell proliferation, migration and cellular invasion by reduction of matriptase and hepsin expression. This in turn led to an increase in the levels of E-cadherin and Slug, and a reduction in the levels of Vimentin, SIP1, Snail and Twist, and hence ER and PR signal transduction in endometrial cancer cells. The levels of HAI-1 and HAI-2 expression were significantly decreased in endometrial cancer specimens relative to the corresponding normal endometrium specimens. Low HAI-1 and HAI-2 expression was a significant predictor for a poor prognosis compared with high HAI-1 and HAI-2 expression. These findings indicate that HAI-1 and HAI-2 could be considered as therapeutic targets and used as favorable prognosis markers for endometrial cancer.

Loss of the matriptase inhibitor HAI-2 during prostate cancer progression

BACKGROUND

Prostate cancer progression is accompanied by increased levels of extracellular proteases that are capable of remodeling the extracellular matrix as well as cleaving and activating growth factors and their receptors that are critically involved in pro-cancerous signaling pathways. The membrane anchored serine protease matriptase (also known as MT-SP1, epithin, and TADG15) has been implicated in prostate cancer. Several studies have demonstrated that the expression of this protease, both on the RNA and protein level is significantly increased during prostate cancer progression. Hepatocyte activator growth factor inhibitor-2 (HAI-2) has recently been identified as a physiological inhibitor of matriptase. It has been proposed that the increase of matriptase with a concomitant loss of its inhibitors may play a critical role in cancer progression.

METHODS

In this study, we used immunohistochemistry to determine the expression of HAI-2 protein in 136 prostate cancer samples, 20 prostate benign prostatic hyperplasia (BPH) samples, and 31 normal or tumor-adjacent prostate samples. Specificity of detection was ensured by using two unrelated HAI-2 antibodies and corresponding non-immune IgG antibodies.

RESULTS

We demonstrate that HAI-2 protein is significantly decreased in malignant lesions as compared to normal and BPH lesions, and that the most poorly differentiated tumors (Gleason score 8-10) have the lowest level of HAI-2 expression.

CONCLUSION

These data suggest that the loss of HAI-2 may be actively involved in prostate cancer progression by causing a reduced inhibitory capacity of proteolysis possibly of the physiological target for HAI-2 matriptase.

Significance of S100A2 and S100A4 Expression in the Progression of Prostate Adenocarcinoma

Purpose

The aim of this study was to investigate the expression pattern of calcium-binding proteins S100A2 and S100A4. We also sought to determine the prognostic value of these markers for patients with prostate adenocarcinoma.

Materials and Methods

Immunohistochemical staining was performed to detect S100A2 and S100A4 expression in 26 tissue samples obtained during transurethral resection from patients with benign prostatic hyperplasia (BPH) and in 67 tissue samples obtained during prostate biopsy and radical prostatectomy from patients with prostate carcinoma. The immunoreactivity of these proteins was stratified on a scale of 0 to 3 and was correlated with the pathologic features of prostate adenocarcinoma.

Results

High expression of S100A2 was observed in the tissue of patients with BPH, whereas low or no expression was observed in prostate cancer (CaP) cells. The protein level of S100A4 was significantly higher in CaP than in BPH cells. The higher level of S100A4 observed in CaP tissue correlated with increasing tumor grade.

Conclusions

Decreased expression of S100A2 and increased expression of S100A4 may be important in the progression of CaP. This finding could aid in identifying aggressive CaP. The simultaneous analysis of S100A2 and S100A4 expression in prostate tissues may be a useful prognostic marker for CaP.

Proteolysis-induced N-terminal ectodomain shedding of the integral membrane glycoprotein CUB domain-containing protein 1 (CDCP1) is accompanied by tyrosine phosphorylation of its C-terminal domain and recruitment of Src and PKCdelta

CUB-domain-containing protein 1 (CDCP1) is an integral membrane glycoprotein with potential as a marker and therapeutic target for a number of cancers. Here we examine mechanisms regulating cellular processing of CDCP1. By analyzing cell lines exclusively passaged non-enzymatically and through use of a panel of protease inhibitors, we demonstrate that full-length 135 kDa CDCP1 is post-translationally processed in a range of cell lines by a mechanism involving serine protease activity, generating a C-terminal 70-kDa fragment. Immunopurification and N-terminal sequencing of this cell-retained fragment and detailed mutagenesis, show that proteolytic processing of CDCP1 occurs at two sites, Arg-368 and Lys-369. We show that the serine protease matriptase is an efficient, but not essential, cellular processor of CDCP1 at Arg-368. Importantly, we also demonstrate that proteolysis induces tyrosine phosphorylation of 70-kDa CDCP1 and recruitment of Src and PKCdelta to this fragment. In addition, Western blot and mass spectroscopy analyses show that an N-terminal 65-kDa CDCP1 ectodomain is shed intact from the cell surface. These data provide new insights into mechanisms regulating CDCP1 and suggest that the biological role of this protein and, potentially, its function in cancer, may be mediated by both 70-kDa cell retained and 65-kDa shed fragments, as well as the full-length 135-kDa protein.

Soluble epithin/PRSS14 secreted from cancer cells contains active angiogenic potential

Epithin (PRSS14/matriptase/ST14), a type II membrane protein, is involved in progression of epithelial cancers and metastasis as well as in the normal epidermal barrier function. When activated, it translocates into the cell-cell contacts and sheds into media. In order to understand the specific mechanism during tumor progression, we tested the angiogenic potential of secreted form of epithin. Epithin produced from the cancer cells shed more in hypoxia and induced motility of endothelial cells. Epithin enhanced the migration and invasion of mouse and bovine endothelial cells without cell proliferation. Furthermore, soluble epithin induced endothelial differentiation in the assay of the human endothelial microvessel-like tube formation and in that of the chicken chorioallantoic membrane. The knock-down of epithin in the 427 thymoma cell line abolished the protease activity of secreted epithin fraction, reduced the invasion of endothelial cells through matrigel, and tube formation activity. Only specific antibodies abolished the migration of endothelial cell and the vessel morphogenesis, suggesting that epithin specifically functions in these systems. Therefore, we propose that the secreted epithin in the hypoxic cancer microenvironment plays a role as a proangiogenic factor, and can be modulated with specific antibodies.

Tumor detection by imaging proteolytic activity

The cell surface protease membrane-type serine protease-1 (MT-SP1), also known as matriptase, is often upregulated in epithelial cancers. We hypothesized that dysregulation of MT-SP1 with regard to its cognate inhibitor hepatocyte growth factor activator inhibitor-1 (HAI-1), a situation that increases proteolytic activity, might be exploited for imaging purposes to differentiate malignant from normal tissue. In this study, we show that MT-SP1 is active on cancer cells and that its activity may be targeted in vivo for tumor detection. A proteolytic activity assay with several MT-SP1-positive human cancer cell lines showed that MT-SP1 antibodies that inhibit recombinant enzyme activity in vitro also bind and inhibit the full-length enzyme expressed on cells. In contrast, in the same assay, MT-SP1-negative cancer cell lines were inactive. Fluorescence microscopy confirmed the cell surface localization of labeled antibodies bound to MT-SP1-positive cells. To evaluate in vivo targeting capability, 0.7 to 2 nmoles of fluorescently labeled antibodies were administered to mice bearing tumors that were positive or negative for MT-SP1. Antibodies localized to MT-SP1-positive tumors (n = 3), permitting visualization of MT-SP1 activity, whereas MT-SP1-negative tumors (n = 2) were not visualized. Our findings define MT-SP1 activity as a useful biomarker to visualize epithelial cancers using a noninvasive antibody-based method.

Unique patterns of molecular profiling between human prostate cancer LNCaP and PC-3 cells

BACKGROUND

Human prostate cancer LNCaP and PC-3 cell lines have been extensively used to study prostate cancer progression and to develop therapeutic agents. Although LNCaP and PC-3 cells are generally assumed to represent early and late stages of prostate cancer, respectively, there is limited information regarding gene expression patterns between these two cell lines and its relationship to prostate cancer.

METHODS

Comprehensive gene expression analysis was performed. Total RNA was isolated from cultured cells and hybridized to Illumina human BeadChips representing 24,526 transcripts. Bioinformatics analysis was applied to identify cell line specific genes as well as biological mechanisms, pathways, and functions related to the genes.

RESULTS

A total of 2,198 genes were differentially expressed between LNCaP and PC-3 cells. Using a robust statistical analysis and high significance criteria, 115 and 188 genes were identified to be unique to LNCaP and PC-3 cells, respectively. LNCaP cells maintained various metabolic pathways including a gene cluster that encodes UDP-glucuronosyltransferases. Several transcription factors including Tal alpha/beta, GATA-1, and c-Myc/Max may be responsible for regulating LNCaP cell specific genes. By contrast, PC-3 cells were characterized by their unique expression of cytoskeleton-related genes and other genes including VEGFC, IL8, and TGF beta 2.

CONCLUSIONS

This study showed that LNCaP and PC-3 cells represent two distinct prostate cancer cell lineages. LNCaP cells retain many prostate cell specific properties, whereas PC-3 cells have acquired a more aggressive phenotype. Future studies for prostate cancer research need to consider similarities and differences between these two cells and their relationship to prostate cancer.

Matriptase: a culprit in cancer?

Pericellular proteases can degrade extracellular matrix proteins and reshape their microenvironment, as well as cleave and activate signaling molecules such as growth factors and their receptors. In this capacity, pericellular proteolysis is essential for multiple biological processes, including development, tissue homeostasis and tissue repair. On the flip side, dysregulated pericellular proteolysis is a hallmark in many pathological conditions including cancer, and is believed to be critically involved in tumor growth, invasion and dissemination of cancer cells to other organs. Matriptase is a member of the family of Type II transmembrane serine proteases, and has been implicated in a variety of epithelial cancers. This review summarizes current knowledge about matriptase and its role in cancer based on expression studies, biochemical characterization, cell-culture based studies and in vivo experiments.

Activation of a membrane-bound serine protease matriptase on the cell surface

Matriptase is a type II transmembrane serine protease. The activation (i.e. conversion of the single-chain pro-form to the disulphide-linked-two-chain active form) of this enzyme is known to occur via a mechanism requiring its catalytic triad. We reported previously that the activated enzyme was produced in the conditioned medium when full-length rat matriptase was expressed in monkey kidney COS-1 cells. The present study aimed to address when and where the matriptase activation occurs. COS-1 cells expressing matriptase were labelled with a membrane-impermeable biotin derivative and then solubilized with Triton. Both activated and non-activated matriptase molecules were detected in the avidin precipitants of Triton extracts, whereas only the non-activated molecules were detected in the flow-through fraction of avidin-precipitation procedure. Single-chain matriptase has been thought to have an inherent activity. Indeed, a secreted single-chain variant of recombinant matriptase bearing mutation at the activation-cleavage site was found to exhibit the activity in hydrolyzing a synthetic peptide substrate at pH 7.5. However, the variant had little activity at pH 5.5, as found in the lumen of post-Golgi secretory vesicles. Altogether, it is concluded that the activation of matriptase may occur when the enzyme reaches the cell surface.

Role of matriptase and proteinase-activated receptor-2 in nonmelanoma skin cancer

Matriptase (membrane-type serine proteinase) was reported to play a role in nonmelanoma skin cancer progression. Moreover, it was shown to stimulate proteinase-activated receptor-2 (PAR(2)) in vitro. Hepatocyte growth factor activator inhibitor-1 (HAI-1), the matriptase inhibitor, is an important regulator of enzyme activity. Therefore, the aim of this study was to elucidate the putative role of matriptase, HAI-1, and PAR(2) in normal human skin, as well as in basal cell carcinomas (BCCs) and squamous cell carcinomas (SCCs). In normal human epidermis, PAR(2) colocalized with matriptase and HAI-1. Immunoreactivity of all proteins was found to be diminished in BCCs. Likewise, PAR(2) immunoreactivity was significantly decreased, whereas matriptase immunoreactivity was enhanced with SCC progression. We could also show that matriptase was complexed to HAI-1 in normal human skin, whereas in SCCs, the enzyme was present in an unassociated form. Both a specific peptide agonist for PAR(2) and the proteinase domain of matriptase were able to induce intracellular calcium mobilization and inhibition of proliferation in cultured HaCaT keratinocytes. In conclusion, our results suggest that PAR(2) is a substrate for matriptase in human skin in vivo. Deregulation of these proteins delineates SCC progression.

Suppression of cFLIP by lupeol, a dietary triterpene, is sufficient to overcome resistance to TRAIL-mediated apoptosis in chemoresistant human pancreatic cancer cells

Overexpression of cellular FLICE-like inhibitory protein (cFLIP) is reported to confer chemoresistance in pancreatic cancer (PaC) cells. This study was designed to investigate the effect of lupeol, a dietary triterpene, on (a) apoptosis of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) therapy-resistant PaC cells overexpressing cFLIP and (b) growth of human pancreatic tumor xenografts in vivo. The effect of lupeol treatment on proliferation and TRAIL/caspase-8/cFLIP machinery in PaC cells was investigated. Next, cFLIP-overexpressing and cFLIP-suppressed cells were tested for sensitivity to recombinant TRAIL therapy in the presence of lupeol. Further, athymic nude mice implanted with AsPC-1 cells were treated with lupeol (40 mg/kg) thrice a week and surrogate biomarkers were evaluated in tumors. Lupeol alone treatment of cells caused (a) decrease in proliferation, (b) induction of caspase-8 and poly(ADP-ribose) polymerase cleavage, and (c) down-regulation of transcriptional activation and expression of cFLIP. Lupeol was observed to increase the TRAIL protein level in cells. Lupeol significantly decreased the viability of AsPC-1 cells both in cFLIP-suppressed cells and in cFLIP-overexpressing cells. Lupeol significantly sensitized chemoresistant PaC cells to undergo apoptosis by recombinant TRAIL. Finally, lupeol significantly reduced the growth of human PaC tumors propagated in athymic nude mice and caused modulation of cFLIP and TRAIL protein levels in tumors. Our findings showed the anticancer efficacy of lupeol with mechanistic rationale against highly chemoresistant human PaC cells. We suggest that lupeol, alone or as an adjuvant to current therapies, could be useful for the management of human PaC.

Protein expression of matriptase and its cognate inhibitor HAI-1 in human prostate cancer: a tissue microarray and automated quantitative analysis

Recent studies have suggested that matriptase, a transmembrane serine protease and its cognate inhibitor hepatocyte growth factor activator inhibitor-1 (HAI-1) are important in the progression of many cancers. Limited quantitative data are available on these proteins in prostate cancer. To validate the roles of matriptase and HAI-1 in prostate cancer and its progression, a prostate cancer tissue microarray was constructed. The tissue microarray includes 41 localized prostate cancers (Pca_local), 18 aggressive prostate cancers, 18 metastatic prostate cancers, 24 benign prostate hyperplasias, 18 high-grade intraepithelial neoplasias (HGPIN), and 41 benign prostate tissues. The cellular expression levels of matriptase and HAI-1 were quantified using automated quantitative analysis. We found that matriptase expression levels were significantly higher in Pca_local (P<0.0001) and HGPIN (P<0.05) compared with benign prostate tissue. Matriptase levels were significantly decreased in metastatic cancer when compared with all other tissue types (P<0.05). Compared with benign prostate tissue, HAI-1 expression levels were significantly higher in all proliferative prostate diseases (benign prostate hyperplasia, HGPIN, localized and aggressive cancers, and metastases) (P<0.001); yet, no significant differences were found in HAI-1 expression levels among the diseased tissue types. These results suggest that an increase of matriptase may be useful as a marker for detection of Pca_local, whereas a decrease of matriptase expression may signal prostate cancer progression. HAI-1 seems to be a marker of prostate epithelial cell proliferation.

Prostatic trypsin-like kallikrein-related peptidases (KLKs) and other prostate-expressed tryptic proteinases as regulators of signalling via proteinase-activated receptors (PARs)

The prostate is a site of high expression of serine proteinases including members of the kallikrein-related peptidase (KLK) family, as well as other secreted and membrane-anchored serine proteinases. It has been known for some time that members of this enzyme family elicit cellular responses by acting directly on cells. More recently, it has been recognised that for serine proteinases with specificity for cleavage after arginine and lysine residues (trypsin-like or tryptic enzymes) these cellular responses are often mediated by cleavage of members of the proteinase-activated receptor (PAR) family--a four member sub-family of G protein-coupled receptors. Here, we review the expression of PARs in prostate, the ability of prostatic trypsin-like KLKs and other prostate-expressed tryptic enzymes to cleave PARs, as well as the prostate cancer-associated consequences of PAR activation. In addition, we explore the dysregulation of trypsin-like serine proteinase activity through the loss of normal inhibitory mechanisms and potential interactions between these dysregulated enzymes leading to aberrant PAR activation, intracellular signalling and cancer-promoting cellular changes.

Purification from human milk of matriptase complexes with secreted serpins: mechanism for inhibition of matriptase other than HAI-1

Matriptase, a type 2 transmembrane serine protease, is predominately expressed by epithelial and carcinoma cells in which hepatocyte growth factor activator inhibitor 1 (HAI-1), a membrane-bound, Kunitz-type serine protease inhibitor, is also expressed. HAI-1 plays dual roles in the regulation of matriptase, as a conventional protease inhibitor and as a factor required for zymogen activation of matriptase. As a consequence, activation of matriptase is immediately followed by HAI-1-mediated inhibition, with the activated matriptase being sequestered into HAI-1 complexes. Matriptase is also expressed by peripheral blood leukocytes, such as monocytes and macrophages; however, in contrast to epithelial cells, monocytes and macrophages were reported not to express HAI-1, suggesting that these leukocytes possess alternate, HAI-1-independent mechanisms regulating the zymogen activation and protease inhibition of matriptase. In the present study, we characterized matriptase complexes of 110 kDa in human milk, which contained no HAI-1 and resisted dissociation in boiling SDS in the absence of reducing agents. These complexes were further purified and dissociated into 80-kDa and 45-kDa fragments by treatment with reducing agents. Proteomic and immunological methods identified the 45-kDa fragment as the noncatalytic domains of matriptase and the 80-kDa fragment as the matriptase serine protease domain covalently linked to one of three different secreted serpin inhibitors: antithrombin III, alpha1-antitrypsin, and alpha2-antiplasmin. Identification of matriptase-serpin inhibitor complexes provides evidence for the first time that the proteolytic activity of matriptase, from those cells that express no or low levels of HAI-1, may be controlled by secreted serpins.

Design and synthesis of novel and potent inhibitors of the type II transmembrane serine protease, matriptase, based upon the sunflower trypsin inhibitor-1

Matriptase, initially isolated from human breast cancer cells in culture, is a member of the emerging class of type II transmembrane serine proteases. Matriptase blockade could potentially modulate tumorigenesis and metastasis in vivo. Sunflower trypsin inhibitor-1 (1, SFTI-1), isolated from sunflower seeds, exhibits very potent matriptase inhibitory activity. On the basis of these findings, we designed and synthesized 13 analogues of the naturally occurring peptide 1 with the intention to explore the structure-activity relationships of this type of bicyclic peptides and to improve inhibitory selectivity and metabolic stability of the disulfide-bridge-containing peptide 1. We discovered that the methylenedithioether-bridged compound 14 demonstrates very potent binding affinity to matriptase. Compound 8 exhibits much better selectivity for inhibition of matriptase versus thrombin, whereas compound 2 becomes a more potent thrombin inhibitor, which can be potentially used as an anticoagulant for prophylaxis and therapy of thromboembolism.

Differences in the rate of lymph node invasion in men with clinically localized prostate cancer might be related to the continent of origin

OBJECTIVE

To test whether the rate of lymph node invasion (LNI) differs between patients treated with radical prostatectomy (RP) at a European or a North American centre.

PATIENTS AND METHODS

In all, 1385 men had RP with bilateral lymphadenectomy for clinically localized prostate cancer (587 from Dallas, Texas and 798 from Milan, Italy). Univariate and multivariate analyses focused on the association between the continent of origin and the rate of LNI, after controlling for prostate-specific antigen (PSA) level, clinical stage, biopsy Gleason sum and the number of examined and removed lymph nodes.

RESULTS

European men had higher PSA levels (9.1 vs 7.8 ng/mL), a higher proportion of palpable cancers (44.5 vs 32.8%), more nodes removed (mean 14.9 vs 7.8) and a higher rate of LNI (9.0% vs 1.2%; all differences P < 0.001). In multivariate analyses that controlled for PSA level and clinical variables, European men had an 8.9-fold higher risk of LNI (P < 0.001) than their counterparts from the USA. Among preoperative variables, the continent of origin was the third most informative predictor of LNI (67.5%), after biopsy Gleason sum (74.3%) and the number of examined lymph nodes (71.0%), and improved the ability to predict LNI by 4.7%.

CONCLUSION

Men treated at a European centre had a 7.3-8.9-fold higher rate of LNI, despite adjusting for all clinical and pathological variables. It remains to be shown what predisposes European men to a higher rate of LNI.

Mapping the human proteome for non-redundant peptide islands

We describe immune-proteome structures using libraries of protein fragments that define a structural immunological alphabet. We propose and validate such an alphabet as i) composed of letters of five consecutive amino acids, pentapeptide units being sufficient minimal antigenic determinants in a protein, and ii) characterized by low-similarity to human proteins, so representing structures unknown to the host and potentially able to evoke an immune response. In this context, we have thoroughly sifted through the entire human proteome searching for non-redundant protein motifs. Here, for the first time, a complete sequence redundancy dissection of the human proteome has been conducted. The non-redundant peptide islands in the human proteome have been quantified and catalogued according to the amino acid length. The library of uniquely occurring n-peptide sequences that was obtained is characterized by a logarithmic decrease of the number of non-redundant peptides as a function of the peptide length. This library represents a highly specific catalogue of molecular protein signatures, the possible use of which in cancer/autoimmunity research is discussed, with a major focus on non-redundant dodecamer sequences.

Autoactivation of matriptase in vitro: requirement for biomembrane and LDL receptor domain

In live cells, autoactivation of matriptase, a membrane-bound serine protease, can be induced by lysophospholipids, androgens, and the polyanionic compound suramin. These structurally distinct chemicals induce different signaling pathways and cellular events that somehow, in a cell type-specific manner, lead to activation of matriptase immediately followed by inhibition of matriptase by hepatocyte growth factor activator inhibitor 1 (HAI-1). In the current study, we established an analogous matriptase autoactivation system in an in vitro cell-free setting and showed that a burst of matriptase activation and HAI-1-mediated inhibition spontaneously occurred in the insoluble fractions of cell homogenates and that this in vitro activation could be attenuated by a soluble suppressive factor(s) in cytosolic fractions. Immunofluorescence staining and subcellular fractionation studies revealed that matriptase activation occurred in the perinuclear regions. Solubilization of matriptase from cell homogenates by Triton X-100 or sonication of cell homogenates completely inhibited the effect, suggesting that matriptase activation requires proper lipid bilayer microenvironments, potentially allowing appropriate interactions of matriptase zymogens with HAI-1 and other components. Matriptase activation occurred in a narrow pH range (from pH 5.2 to 7.2), with a sharp increase in activation at the transition from pH 5.2 to 5.4, and could be completely suppressed by moderately increased ionic strength. Protease inhibitors only modestly affected activation, whereas 30 nM (5 microg/ml) of anti-matriptase LDL receptor domain 3 monoclonal antibodies completely blocked activation. These atypical biochemical features are consistent with a mechanism for autoactivation of matriptase that requires protein-protein interactions but not active proteases.

S100A4 accelerates tumorigenesis and invasion of human prostate cancer through the transcriptional regulation of matrix metalloproteinase 9

We previously showed that the calcium-binding protein S100A4 is overexpressed during the progression of prostate cancer (CaP) in humans and in the TRAMP (transgenic adenocarcinoma of the mouse prostate) mouse model. We tested a hypothesis that the S100A4 gene plays a role in the invasiveness of human CaP and may be associated with its metastatic spread. We observed that siRNA-mediated suppression of the S100A4 gene significantly reduced the proliferative and invasive capability of the highly invasive CaP cells PC-3. We evaluated the mechanism through which the S100A4 gene controls invasiveness of cells by using a macroarray containing 96 well characterized metastatic genes. We found that matrix metalloproteinase 9 (MMP-9) and its tissue inhibitor (TIMP-1) were highly responsive to S100A4 gene suppression. Furthermore, S100A4 suppression significantly reduced the expression and proteolytic activity of MMP-9. By employing an MMP-9-promoter reporter, we observed a significant reduction in the transcriptional activation of the MMP-9 gene in S100A4-siRNA-transfected cells. Cells overexpressing the S100A4 gene (when transfected with pcDNA3.1-S100A4 plasmid) also significantly expressed MMP-9 and TIMP-1 genes with increased proteolytic activity of MMP-9 concomitant to increased transcriptional activation of the MMP-9 gene. S100A4-siRNA-transfected cells exhibited a reduced rate of tumor growth under in vivo conditions. Our data demonstrate that the S100A4 gene controls the invasive potential of human CaP cells through regulation of MMP-9 and that this association may contribute to metastasis of CaP cells. We suggest that S100A4 could be used as a biomarker for CaP progression and a novel therapeutic or chemopreventive target for human CaP treatment.

Secondary amides of sulfonylated 3-amidinophenylalanine. New potent and selective inhibitors of matriptase

Matriptase is an epithelium-derived type II transmembrane serine protease and has been implicated in the activation of substrates such as pro-HGF/SF and pro-uPA, which are likely involved in tumor progression and metastasis. Through screening, we have identified bis-basic secondary amides of sulfonylated 3-amidinophenylalanine as matriptase inhibitors. X-ray analyses of analogues 8 and 31 in complex with matriptase revealed that these inhibitors occupy, in addition to part of the previously described S4-binding site, the cleft formed by the molecular surface and the unique 60 loop of matriptase. Therefore, optimization of the inhibitors included the incorporation of appropriate sulfonyl substituents that could improve binding of these inhibitors into both characteristic matriptase subsites. The most potent derivatives inhibit matriptase highly selective with K(i) values below 5 nM. Molecular modeling revealed that their improved affinity results from interaction with the S4 site of matriptase. Analogues 8 and 59 were studied in an orthotopic xenograft mouse model of prostate cancer. Compared to control, both inhibitors reduced tumor growth, as well as tumor dissemination.

Pro-urokinase-type plasminogen activator is a substrate for hepsin

Hepsin, a type II transmembrane serine protease, is strongly up-regulated in prostate cancer. Hepsin overexpression in a mouse prostate cancer model resulted in tumor progression and metastasis, associated with basement membrane disorganization. We investigated whether hepsin enzymatic activity was linked to the basement membrane defects by examining its ability to initiate the plasminogen/plasmin proteolytic pathway. Because plasminogen is not processed by hepsin, we investigated the upstream activators, urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator. Enzymatic assays with a recombinant soluble form of hepsin demonstrated that hepsin did not cleave pro-tissue-type plasminogen activator but efficiently converted pro-uPA into high molecular weight uPA by cleavage at the Lys158-Ile159 (P1-P1') peptide bond. uPA generated by hepsin displayed enzymatic activity toward small synthetic and macromolecular substrates indistinguishable from uPA produced by plasmin. The catalytic efficiency of pro-uPA activation by hepsin (kcat/Km 4.8 x 10(5) m(-1) s(-1)) was similar to that of plasmin, which is considered the most potent pro-uPA activator and was about 6-fold higher than that of matriptase. Conversion of pro-uPA was also demonstrated with cell surface-expressed full-length hepsin. A stable hepsinoverexpressing LnCaP cell line converted pro-uPA into high molecular weight uPA at a rate of 6.6 +/- 1.9 nm uPA h(-1), which was about 3-fold higher than LnCaP cells expressing lower hepsin levels on their surface. In conclusion, the ability of hepsin to efficiently activate pro-uPA suggests that it may initiate plasmin-mediated proteolytic pathways at the tumor/stroma interface that lead to basement membrane disruption and tumor progression.